8 The Colorado Experiment Station 
nitric acid or nitrates, they would do us a great service, but they 
have built up too much of these compounds in many places. The 
brown color is not due to the presence of the nitrates, for they are 
colorless, but to a coloring matter formed by these germs. This 
coloring matter is soluble in water and may be partially, or at 
times possibly wholly, washed into the soil with the nitrates. The 
brown spots and soils scattered throughout our valleys and irrigated 
sections have been the cause of many inquiries during recent years. 
There are some instances in which the color may not be due to 
these germs but they are the cause of almost all of it. This is not 
the only germ which converts the atmospheric nitrogen into nitric 
acid or effects the fixation of nitrogen, as it is designated, but it 
is a common one in our soils. 
It is not the brown color that does the damage, but it is the 
nitrates which are formed by the same agent in quantities large 
enough to kill the trees and other vegetation. It is the nitrates that 
produce the mealiness of the soil, at least nitrate or soda applied to 
the soil produces the same condition. Nitrate of soda applied to 
apple trees in excessive quantities, produces a burning of the leaves 
and the death of the tree in a manner similar to that shown by the 
trees in the orchards. 
The amounts of nitrates found in the various samples of soils 
taken from affected areas strike one as almost incredible. We found 
in a sample of surface soil 6.54 per cent of sodic nitrate. This is 
the largest amount found in any sample and indicates the presence 
of nearly eleven tons in an acre of ground taken to a depth of one 
inch. Many samples indicate the presence of extremely large 
amounts of nitrates in these soils. 
While these nitrates in small quantities are beneficial to vegeta¬ 
tion they are poisonous when applied in larger quantities. The 
death of trees, for instance, was due to excessive quantities of ni¬ 
trates formed in the soil. 
